Children and junk food

I need advice my sister has a 8 year old son and ever since he was a baby he has been fed on only Gregg's sausage rolls sometimes two for dinner every night , McDonald's happy meals and occasionally adult meals , my nephew ears nothing else apart from this for dinners and his snacks only include crisps chocolate and fizzy drinks we have on occasion got on to her about this but she just says is it your kid deal with your own !! I'm so worried about my nephew as you can tell he is overweight and un active for his age and it worries me what can I do to Help ? I never feed my kids junk unless it's a treat but my nephew won't eat anything else he makes his self sick but I just think he's been let away with telling him mum what he's eating and not eating for too long it makes me do angry but what am I going to do she says it's non of m business

There's not much you can do really. You've told her the issue and she refused to listen. I think your sister will listen if it comes from the HV, gp or school nurse that his diet is affecting his health.. Will she take advice from your mum or any family members?